Money Market Fund: How Short-Term Cash Parking Works

Key Takeaways

• Money market funds are Rule 2a-7 mutual funds, not bank accounts; they are not FDIC-insured and can in theory break the $1.00 stable price.
• The 2023 SEC reforms raised daily liquid assets to 25% and weekly to 50%, and removed the redemption gate authority in place since 2014.
• Investors confuse money market funds with money market bank deposit accounts; only the bank deposit carries FDIC insurance.
• Government, prime, and municipal funds carry meaningfully different credit and tax profiles that matter in stress and in high-tax brackets.

What It Is

Money market funds are regulated under Rule 2a-7 of the Investment Company Act of 1940. The rule sets strict limits on the maturity, credit quality, diversification, and liquidity of holdings so the fund can offer daily liquidity and, for qualifying funds, a stable 1.00 USD net asset value.

There are three main types:

• Government funds. Invest almost entirely in Treasury bills, repurchase agreements backed by Treasuries, and other US government securities.
• Prime funds. Invest in high-quality corporate debt, including commercial paper and certificates of deposit, along with government paper.
• Municipal (tax-exempt) funds. Hold short-term municipal debt; income is often exempt from federal tax.

Funds are further classified as retail or institutional based on who can buy shares.

The Intuition

Investors need somewhere safe to hold cash that earns more than a bank checking account. Treasuries yield a rate, but individual bills mature on fixed dates. A money market fund bundles hundreds of short-term instruments, spreads them across issuers, and reprices yield daily. The stable 1.00 USD share price, when available, makes the fund behave like a high-yield cash account.

"Stable" is not the same as "guaranteed." A money market fund is not a bank deposit and is not FDIC-insured. In 2008, the Reserve Primary Fund "broke the buck" after Lehman Brothers filed for bankruptcy, which triggered the first round of money market reform.

How It Works

Rule 2a-7 imposes limits across several axes. A money market fund must:

• Maintain a dollar-weighted average portfolio maturity within tight limits.
• Hold only high-quality short-term debt, with diversification caps on any single issuer.
• Mark to market regularly to ensure the stable price remains supported by actual asset values.
• Maintain substantial holdings of daily and weekly liquid assets.

The SEC adopted significant amendments to Rule 2a-7 in July 2023. Key changes:

• Higher liquidity minimums. Daily liquid assets raised to 25 percent and weekly liquid assets to 50 percent of fund assets.
• Redemption gates removed. Funds can no longer temporarily suspend redemptions when liquidity falls below a threshold.
• Mandatory liquidity fee for institutional prime and institutional tax-exempt funds. Triggered when daily net redemptions exceed 5 percent of net assets unless liquidity costs are de minimis.
• Negative interest rate mechanics. Retail and government funds may either float the NAV or reduce share count to maintain a stable price, with board oversight.

Retail prime and retail tax-exempt funds can still target a stable 1.00 USD NAV. Institutional prime and institutional tax-exempt funds have floated NAVs since the 2016 reform and remain floating-NAV under the current rules.

Worked Example

An investor moves 100,000 USD from a checking account paying 0.05 percent into a government money market fund yielding 5.10 percent (7-day yield).

Annual income: 100,000 x 0.0510 = 5,100 USD, compounded daily in practice. The share price stays at 1.00 USD and the investor sees the yield as daily dividends reinvested.

If the Fed cuts rates sharply, the fund's 7-day yield falls in lockstep, perhaps to 3.00 percent within a few months, because the portfolio repositions into new short-dated paper at lower yields. The stable 1.00 USD price still holds, but income drops.

If the investor holds an institutional prime fund and tries to redeem a large block on a day the fund sees more than 5 percent net outflows with non-trivial liquidity costs, a liquidity fee of up to 2 percent may apply. That is the fee framework the 2023 reform put in place.

Common Mistakes

• Treating a money market fund as FDIC-insured. It is a mutual fund. Principal is not guaranteed by the US government or any agency.
• Confusing a money market fund with a money market account. A money market deposit account at a bank is FDIC-insured. A money market fund is not. The names sound alike but the products are different.
• Ignoring the fund type. Government funds carry less credit risk than prime funds. In a stress episode, the two can behave quite differently.
• Chasing a 10 basis point yield advantage. Small yield differences often reflect small credit or liquidity differences that matter more in a crisis than in calm markets.
• Forgetting taxes. A prime fund's yield is fully taxable. A Treasury-only government fund's income may be state tax-exempt. A municipal fund's income may be federal tax-exempt. After-tax yield is what matters.

Frequently Asked Questions

Q: What is a money market fund in simple terms? A money market fund is a mutual fund that buys short-duration, high-quality debt instruments and targets a stable $1.00 share price. It pays a yield close to prevailing short-term interest rates and is the standard cash-parking vehicle inside brokerage accounts.

Q: How does a money market fund affect investment decisions? It sets the floor return on uninvested cash and determines the opportunity cost of holding liquidity. When short-term rates are high, moving cash from a low-yield bank account to a government money market fund can add meaningful risk-free return without complexity.

Q: What is a real-world example of money market fund risk? In 2008, the Reserve Primary Fund broke the dollar after Lehman Brothers failed, triggering the first major money market reform. Investors who assumed the $1.00 price was guaranteed discovered it was a fund-management target, not a legal guarantee.

Q: How can investors choose the right money market fund type? In a high-tax bracket, compare after-tax yields by calculating the taxable equivalent of municipal fund yields. If holding inside a tax-deferred account, choose the fund with the best pre-tax yield. Avoid chasing tiny yield advantages that reflect small credit differences.

Q: How is a money market fund different from a money market bank account? A money market deposit account at a bank is FDIC-insured up to $250,000 per depositor per bank. A money market mutual fund is not insured. The names are nearly identical, but one is a deposit account and one is a regulated investment company.

Sources

1. SEC. "Money Market Fund Reforms; Form PF Reporting Requirements (Final Rule S7-22-21)." https://www.sec.gov/rules-regulations/2023/07/s7-22-21
2. SEC Press Release. "SEC Adopts Money Market Fund Reforms." July 2023. https://www.sec.gov/news/press-release/2023-129
3. Federal Register. "Money Market Fund Reforms (2023-15124)." August 3, 2023. https://www.federalregister.gov/documents/2023/08/03/2023-15124/money-market-fund-reforms-form-pf-reporting-requirements-for-large-liquidity-fund-advisers-technical
4. Harvard Law School Forum on Corporate Governance. "The SEC's Money Market Fund Reforms." August 2023. https://corpgov.law.harvard.edu/2023/08/22/the-secs-money-market-fund-reforms/

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.